Once a petroleum well has been drilled and cased, it may be desirable to drill one or more additional sidetracked well bores that branch off, or deviate, from the primary well bore. Such multilateral well bores are typically directed toward different targets within the surrounding formation, with the intent of increasing the production output of the well.
Multilateral technology provides operators several benefits and economic advantages, such as tapping isolated pockets of hydrocarbons that might otherwise be left unproduced, and improving reservoir drainage so as to increase the volume of recoverable reserves and enhance the economics of marginal pay zones. By utilizing multilateral technology, multiple reservoirs can also be drained simultaneously, and thin production intervals that might be uneconomical to produce alone may become economical when produced together. Multiple completions from one well bore also facilitate heavy oil drainage.
In addition to production cost savings, development costs also decrease through the use of existing infrastructure, such as surface equipment and the primary well bore. Multilateral technology expands platform capabilities where slots are limited and eliminates spacing problems by allowing more drain holes to be added within a reservoir. In addition, by sidetracking damaged formations or completions, the life of existing wells can be extended. For example, sidetracked well bores may be drilled below a problem area once the casing has been set, thereby reducing the risk of drilling through troubled zones. Finally, multilateral completions accommodate more wells with fewer footprints, making them ideal for environmentally sensitive or challenging areas.
To maximize the productivity of multilateral completions, it is desirable to enlarge at least some of the sidetracked well bores to thereby increase the production flow area through such boreholes. By drilling a sidetracked well bore through a casing window, and then enlarging the sidetracked well bore beyond the casing window, the far reaches of the reservoir can be reached with a comparatively larger diameter borehole, thereby providing more flow area for the production of oil and gas.
However, conventional methods for drilling an enlarged sidetracked well bore require multiple trips into the primary well bore. For example, a first trip may be made into the primary well bore to run and set an anchored whipstock comprising an inclined face that guides a window mill radially outwardly into the casing to cut a window in the casing. The window mill is then tripped out of the primary well bore, and a drill bit is lowered in a second trip to drill the sidetracked well bore through the casing window. The diameter of the sidetracked well bore is thereby limited by the diameter or gauge of the drill bit that can extend through the casing window. Once the sidetracked well bore has been drilled, the drill bit is then tripped out of the primary well bore, and another drilling assembly, such as a drill bit followed by a reamer, for example, is lowered in a third trip into the primary well bore to extend and enlarge the sidetracked well bore. It is both expensive and time consuming for an operator to make multiple trips into a primary well bore to drill and enlarge a single sidetracked well bore, and such concerns are only compounded when drilling more than one sidetracked well bore in a multilateral completion.
Thus, in recent years, a window milling bit comprising diamond cutters has been developed that is operable to mill a window through a standard metal casing and drill a sidetracked well bore through the casing window in a single trip into the primary well bore. This window milling bit with diamond cutters thereby eliminates one trip into the primary well bore, but at least another trip is still required to enlarge the sidetracked well bore. Therefore, a need exists for apparatus and methods that enable milling a window through a casing in a primary well bore, and drilling an enlarged sidetracked well bore through the casing window in one trip into the well bore.
To perform such a sidetracking operation, it would also be advantageous to provide a single cutting device capable of both milling the casing and drilling an enlarged sidetracked well bore. Such a device is desirable to provide a more compact drilling assembly for increased maneuverability and control while drilling the enlarged sidetracked well bore through the casing window.
Further, when operating a window milling bit to mill casing and drill formation, whether drilling an enlarged borehole or not, the cutting structures on such a bit may be worn down during operation. Thus, a need exists for a cutting device with multiple cutting structures adapted to recover gauge as the device is used to mill through casing and/or drill into formation. In addition, it may be desirable for the window milling bit to have at least a first cutting structure to perform the milling operation, and at least a second cutting structure to perform the drilling operation. Thus, a need exists for a cutting device with multiple cutting structures wherein at least one of the cutting structures is selectively presented when desired by the operator. Such a cutting device would be useful for many other purposes, including drilling through different types of formation rock, or replacing worn cutting structures when drilling a lengthy borehole, for example.
The present invention addresses the deficiencies of the prior art.